Disease model interpretation:
DSVs: Late blight risk can be modeled using disease severity values (DSVs). First, select your nearest weather station. On the chart shown, highlight the date of your last spray and note the cumulative DSVs at that point. Then subtract that number from the most recent cumulative DSV value to get the accumulated DSVs since your last spray. When this value exceeds 18, late blight management action is recommended. You can download each chart by clicking on the menu button on the upper right corner. Visit VDIFN and select the Late Blight model for a statewide map of late blight risk.
P-Days: Early blight risk is elevated after 300 P-Days (physiological days) have accumulated after crop emergence. Early blight management actions are recommended beyond that point. You may need to subtract accumulated P-Days from prior to your specific crop emergence date from the weather station report. Visit VDIFN and select the Early Blight model for a statewide map of P-Days and early blight risk.